1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of driving the same, and more particularly, to a field-sequential color (FSC LCD) LCD device with improved brightness and resolution and a method of driving a FSC LCD.
2. Discussion of the Related Art
In general, related art cathode ray tubes (CRT) are widely as display devices for televisions, measuring apparatuses, and information terminals. Since the related art CRTs have increased weight and size, reducing these measurements of the related art CRTs is difficult, hence, it is impossible for some electronic apparatus to be made smaller and lighter. Accordingly, demand for LCD devices which are light, small, and consume less power is rising, and the LCD devices are actively replacing the related art CRTs.
According to the driving principle of the LCDs, optical anisotropy and polarizability of liquid crystal materials are used. Since the liquid crystal materials have the shape of a round rod and has a long axis and a short axis, liquid crystal materials are arranged in a predetermined direction. By applying the electric filed to the liquid crystal materials, the direction of the liquid crystal materials is controlled. When the direction in which the liquid crystal materials are arranged is arbitrarily controlled, back-light units provided on the back surface of a LCD panel selectively transmits or selectively intercepts light in accordance with the direction of the liquid crystal materials' arrangement, so that color images can be displayed.
FIG. 1 is a side view showing the structure of related art LCD device.
Referring to FIG. 1, an LCD device 10 includes a first substrate 20 and a second substrate 40 that are attached to each other having a certain cell-gap, a liquid crystal layer 30 disposed in a space between the first substrate 20 and the second substrate 40, and back-lights 50 produced on the rear surface of the second substrate 40 to supply light to a LCD panel 15.
A black matrix 22 is disposed along the outlines of pixels. The black matrix 22 partitions the pixels to a first portion that transmits light and a second portion that intercepts light. And, the black matrix 22 is disposed under a transparent substrate 21 of the first substrate 20. Red, green, and blue color filters 23 are disposed under the transparent substrate 21.
Transparent common electrodes 24 applying the electric field to the liquid crystal layer 30 are disposed under the color filters 23. On the other hand, thin film transistors (TFT), transparent pixel electrodes 42 and the transparent common electrodes 24 are disposed on a transparent substrate 41 of the first substrate 40. The TFTs function as switches. The transparent pixel electrodes 42 apply the electric field to the liquid crystal layer 30 by receiving signals from the TFTs.
In addition, a plurality of gate lines separated from each other having regular intervals and a plurality of data lines separated from each other having regular intervals intersect each other to define the pixels in the square regions. The gate lines are arranged in a horizontal direction, and the data lines are arranged in a vertical direction. The pixels are arranged on the second substrate 40 in a matrix and include the pixel electrode 42. The TFTs include gate electrodes electrically connected to the gate lines, source electrodes electrically connected to the data lines, and drain electrodes electrically connected to the pixel electrodes 42.
The related art LCD device as described above has the following disadvantages. First, it has a low transmittance of light. Only about 33% of light manages to pass through the color filters 23. Therefore, it is necessary to generate more intensive light to improve the brightness of the LCD device. As a result, power consumption increases. In addition, the color filters 23 used in the LCD device are more expensive than other materials, thus, the manufacturing cost of the LCD device increases. To solve the above-described problems, a FSC LCD device capable of realizing full colors without using the color filters 23 is suggested.
In general, when the related art LCD device is driven, the back-lights of the LCD device supplies white light in a state where the back-lights are turned on. In contrast, according to the FSC LCD device having the related art structure, a red, green and blue back-lights illuminate a pixel frame at predetermined intervals so that color images are displayed.
FIG. 2 is a side view of the FSC LCD device having the related art structure.
Referring to FIG. 2, a FSC LCD device 60 includes a first substrate 70 and a second substrate 90 that are attached to each other having a cell gap, a liquid crystal layer 80 disposed in a space between the first substrate 70 and the second substrate 90, and a red (R), green (G), and blue (B) back-lights 100 positioned on the rear surface of the second substrate 90 to supply red, green, and blue light to a LCD panel 65.
A black matrix 72 formed along the outlines of pixels partitions the pixels into portions that transmit light and portions that intercept light. The black matrix 72 is disposed under a transparent substrate 71 of the first substrate 70. Transparent common electrodes 73 that are one-side electrodes for applying an electric field to the liquid crystal layer 80 are also disposed under the transparent substrate 71.
Thin film transistors (TFT), transparent pixel electrodes 92, and the transparent common electrodes 73 are disposed on a transparent substrate 91 of the second substrate 90, where TFTs function as switches. The transparent pixel electrode 92 applies the electric field to the liquid crystal layer 80 by receiving signals from the TFTs.
The FSC LCD device 60 having the related art structure is different from a related art LCD device in that color filters are not required, and that red, green, and blue light sources are separately turned on, for example, red (R), green (G), and blue (B) back-lights 100 are applied individually. The supplied red, green, and blue light flash 60 times per a second. However, it is visually sensed that the red, green, and blue lights are continuously emitted. For example, when the red light is first emitted and then the blue light is emitted in a short time, due to afterimage effect, it is sensed that violet light is emitted.
FIG. 3 is a schematic view describing the driving of the FSC LCD device having the related art structure where TFTs are manufactured on a substrate.
Referring to FIG. 3, a plurality of horizontally arranged gate lines 101 and a plurality of vertically arranged data lines 102 intersect each other to define pixels in the square portions. Each of the TFTs is provided in one corner of each of a plurality of pixels. In addition, pixel electrodes 103 electrically connected to the TFTs are provided in the each of the plurality of pixels. The FSC LCD device having the related art structure is driven by sequentially applying a scan signal to the gate lines 101 and applying image information to the data lines 102.
As illustrated in the drawing, when a gate driving unit applies the scan signal to an Nth gate line 101, the TFTs of the pixels electrically connected to the Nth gate line 101 are simultaneously turned on and the image information supplied from the data lines 102 is applied to the pixel electrodes 103 through the turned on TFTs.
The pixel electrodes 103 are disposed on the above-described first substrate 70 of FIG. 2 to apply an electric field to the liquid crystal layer 80. The common electrodes 73 to which a common voltage is applied, is also disposed on the first substrate 70. When an electric field is applied to the liquid crystal layer 80, the direction of the liquid crystal materials arrangement in the liquid crystal layer 80 changes, and the red, green, and blue back-lights 100 are sequentially turned on. The red, green, and blue light are selectively transmitted through the liquid crystal layer 80 in accordance with the directions of the liquid crystal materials arrangement to realize color images. That is, the red, green, and blue back-lights 100 flash once on a panel in a frame during the entire driving period of the FSC LCD device having the related art structure.
According to the FSC LCD device having the related art structure, a TFT scanning period for sequentially applying the scan signal to the gate lines and for applying image information to the data lines, a liquid crystal response period for re-arranging the liquid crystal materials of the liquid crystal layer, and a flashing period for turning on the back-lights are performed with respect to the red, green, and blue back-lights. Therefore, with the driving mechanism as described above, the brightness of an image increases in a unit length of the flashing period. However, since the TFT scanning period and the liquid crystal response period must be performed three times to display one frame of an image, there is a limit to increasing the length of the flashing period. Accordingly, the brightness of the FSC LCD device having the related art structure does not have a substantial improvement as compared to the related art LCD devices where color filters are used. Furthermore, when the FSC LCD device having the related art structure has a higher resolution and an increased panel area, number of gate lines increases, and the TFT scanning period becomes longer while the liquid crystal response period is maintained. Thus, the length of the flashing period must be reduced to display one frame of the image.
As a result, for the FSC LCD device having the related art structure that has the higher resolution and the increased panel area, the length of the flashing period must be reduced. This results in a reduction of brightness, and making it difficult to display high quality images. As a result, the FSC LCD device having the related art structure is not desirable to be used in the LCD devices having the high resolution and the increased panel area.